Flame-retardant compositions based on ethylene polymers and inorganic fillers are known and used as coverings for electrical cables. In particular, Patents EP 326,775 and EP 406,035 describe compositions containing inorganic fillers, such as magnesium hydroxide or aluminum hydroxide, and crosslinked ethylene polymers. These compositions do not contain polyamide. For some electrical cables, it is necessary for the mechanical properties and the resistance to solvents to be better than those of polyethylene-based compositions.
Patent EP 564,338 describes a multi-phase thermoplastic composition based on polyamide resin containing an ethylene polymer with epoxide functional groups. The sole objective of this patent is to improve the low-temperature impact strength. The composition can contain fillers in order to give it rigidity. No mention is made of the distribution of the flame retardant agent which prevents the properties of the polyamide matrix from being detrimentally affected.
Application JP 05093108 A, published on Apr. 16, 1993, describes flame-retardant compositions for electrical cables based (i) on polyethylene or ethylene copolymers, (ii) on polyamide in order to resist wear, (iii) on functionalized copolymers in order to make the polyethylene and the polyamide compatible and finally on flame-retardant agents. These compositions, based essentially on polyethylene, have neither the mechanical properties of the present invention nor their resistance to oil.
European Application EP 258,040 describes alloys (i) of polyamide and (ii) of an ethylene-alkyl acrylate-maleic anhydride copolymer which are optionally ionomerized and which contain an agent capable of crosslinking (i) or (ii). Moreover, no mention is made nor are any examples given of the incorporation of flame-retardant agents.
EP 532,122 describes compositions comprising polyamide, functionalized polypropylene and magnesium hydroxide having a good surface appearance after molding. These compositions have a very high magnesium hydroxide content and the flexural modulus varies from 5,800 to 8,400 MPa, which characterizes a material which is too rigid to be able, for example, to insulate electrical cables. Moreover, this composition has poor resistance to oils and to acids.